Investigating fire-induced ozone production from local to global scales

Abstract. Tropospheric ozone (O3) production from wildfires is highly uncertain; previous studies have identified both production and loss of O3 in fire-influenced air masses. To capture the total ozone production attributable to a smoke plume, we bridge the gap between near-field fire chemistry and aged smoke in the remote troposphere. Using airborne measurements from several campaigns, we find that fire-ozone production increases with age, with a regime transition from NOx-saturated to NOx-limited conditions, showing that O3 production in aged plumes is controlled by nitrogen oxides (NOx). Observations in fresh smoke show that suppressed photochemistry reduces O3 production by ~70% in units of ppb Ox per ppm CO. Anthropogenic NOx injection into VOC-rich fire plumes drives additional O3 production, exceeding 50 ppb above background in extreme cases. Using a box model, we explore the sensitivity of O3 production to fire emissions and chemical parameters, demonstrating the importance of aerosol-induced photochemical suppression over heterogeneous HO₂ uptake, validating HONO's role as an oxidant precursor, and confirming evolving NOx sensitivity. We evaluate GEOS-Chem's performance against these observations, finding that the model captures fire-induced O3 enhancements at older ages but overestimates near-field enhancements, fails to capture fire emission magnitude and variability, and misses the chemical regime transition. These discrepancies bias normalized ozone production (∆O3/∆CO) across plume lifetime. GEOS-Chem attributes 2.4% of the global tropospheric ozone burden and 3.1% of surface ozone concentrations to fire emissions in 2020, with stronger impacts in regions of frequent burning.